Slow tissue on gas from stops

[dmaziuk]

Could it be that because they dived LE model, m-values were not "all that remains"? Enquiring minds are wondering.

 

[Patoux01]

Again, if one believes there is nothing to deep stop theory, all that remains is m-values.
That's why when I meet divers who say things on the line of deep stop theory being bogus, I might well point out that they're probably not using GF100/100 because they don't truly believe gas mechanics theory is bogus at all.

But eh, I might not understand deco, but what would it be that makes using *any* GF make buhlmann GF a bubble model? I mean, I have a nice drawing here that shows that GF simply takes the m-value line and moves it a bit around, but nowhere does it seem to relate to the "reason" deep stops exist.

 

[UWSojourner]

my point as it relates to discussions on this matter is, if one thinks that "deep stops have been debunked", it begs two obvious questions:

For clarity (which it seems you might be requesting), I think that "deep stops have been debunked", or "deep stops don't work" is a colloquialism of statements like "bubble-model-style deep stops are not efficient", or "current research would lead us to conclude that bubble-model-style deep stops like those generated by popular bubble models (e.g. VPM, RGBM,RD) require more time, not less, to obtain the same level of DCS risk."

But it's not a travesty of logic, after thousands of posts across numerous forums, to speak more concisely and just say "deep stops don't work". Those following along know which models are being discussed.

1) What is a deep stop?
This illustrates well that what we're talking about here, is where the line in the sand is. No-one is saying that "there is scientific proof that deep stops don't work". Just that they've been overemphasised by some margin.

Your argument is just slight of hand. You're yelling "look at deep stops, look at deep stops!" and whispering "you haven't defined deep stops."

But, the NEDU study, for example, tested a bubble model vs. a gas-content model. What it found was that the bubble model's recommendations produced a higher incidence of DCS. And, truly, in the NEDU's study all other things were equal.

Further, after a lot of analysis, the NEDU concluded that the REASON the bubble model failed was due to the deeper stops recommended by the model. Those stops caused more on-gassing in the slower compartments that increased overall supersaturation exposure which increased risk.

That same pattern (i.e. bubble model holding divers deeper for longer periods causing more overall supersaturation exposure) has been shown to repeat itself in bubble models like VPM-B

2) Why not use GF100/100, then?
If "deep stops have been debunked" holds true, then surely, all that remains presently on the table in terms of decompression, is tissue gas supersaturation á la Haldane. If that is the case, logical deduction demands that one should perceive m-values pure as the optimal decompression line. Hence GF100/100. But nobody's doing that.

This is a huge leap. And illogical. A diver says to you, "I don't think I'll dive VPM-B, or RD, due to the deep stops it imposes." and you throw up your hands and say, "Well, then, you have to dive GF100/100!" Really!!??

As has been discussed over and over and over and over ... you can take the same times you're diving with VPM-B and simply reallocate some of that time to shallower stops via another model (e.g. GF) -- same time, shallower profile. And I think MANY divers are doing that.

....

The rest of your post complains that some posts talk in looser language ... well, ok. So what. SB is a discussion over beers, not a formal treatise.

 

[Dan_P]

Ah. My bad. Since you were bringing up that point here on SB, in this thread, I stupidly assumed that you were talking about discussions in here, which in my mind would be appropriate. Bringing in - and misquoting by embellishment - a more than three year post, on another forum, which BTW is well known for quite saltier language than what we see here on Scubaboard, looks pretty much like a strawman argument to me.

I've chosen to attempt a deescalatory approach by illustrating with an example external to this board.
And I don't agree that's a strawman argument at all.

Also, note, I have zero buy-in in regards deep stops per sé, as I:

1) Am under no obligation to use them in training.
2) Am able to adjust deep stop emphasis on my dives, at my own discression.
3) Am planning my dives not fully based on physiology but also other factors, like logistics.

@UWSojourner if we look at Doolette's explanation of why the NEDU study pushed to higher risk, it makes sense - but doesn't show that deep stops are unsafe;
On the above basis, one might argue that they're suboptimal, which is a fair argument; or counterargue, well, deep air, cold, and so on and so forth, which I also think would be reasonable, and we could all have that discussion (again, again, again).
But my point, rather, is that the difference, the nuance of that discussion, seems to be unclear to some (online and off) - and I think that's an issue.

I don't believe there's fairness in calling it a slight of hand if I say "what is a deep stop?" strikes at the heart of the conversation.
I feel that the question very aptly highlights exactly what we're discussing.

As for GF100/100, you're drawing a parallel across RD and VPM and deep stops, which prerequisites your logic that anyone participating in the conversation and uses the term "deep stop", knows all the ins and outs of the debate.
In my experience, that's not the case - particularly in the offline domain.

But that's precisely the point, if deep stop theory, bubble mechanics, is out the window, what have you left?
M-values.
Hardly a controversial statement?

 

[UWSojourner]

@UWSojourner if we look at Doolette's explanation of why the NEDU study pushed to higher risk, it makes sense - but doesn't show that deep stops are unsafe;
On the above basis, one might argue that they're suboptimal, which is a fair argument;

Actually, that has been the ONLY argument made. Deep stops are "suboptimal", "inefficient", "counterproductive to safety".

If someone summarizes that as "unsafe", then perhaps its not precise. But they might really mean "not as safe as another option I have using the same decompression time". Then it's fine.

As for GF100/100, you're drawing a parallel across RD and VPM and deep stops, which prerequisites your logic that anyone participating in the conversation and uses the term "deep stop", knows all the ins and outs of the debate.
In my experience, that's not the case - particularly in the offline domain.

Let me put it this way. If I heard someone say, "Deep stops are unsafe" and another person say, "Deep stops are not unsafe and you have to use GF100/100 if you say that" I would conclude that it was person 2 who didn't understnad the "ins and outs of the debate."

But that's precisely the point, if deep stop theory, bubble mechanics, is out the window, what have you left?

The sure knowledge that one of the theoretical, but untested, and near religious mass followings in the technical diving world is over .

Actually, though, bubble mechanics is not out the window. The simplistic versions unrelated to physiology are probably out the window (e.g. VPM-B). But eventually a proper understanding of how bubbles form and are removed by the body during decompression has to move toward the experimental results that produce M-values. Bubble theory just isn't there yet.

But when it has "arrived", current research suggests it will be producing profiles that are shallower (i.e. more like those produced by GF40/X, GF50/X, etc. than by today's more suspect bubble models like VPM-B).

 

[Dan_P]

Actually, that has been the ONLY argument made. Deep stops are "suboptimal", "inefficient", "counterproductive to safety".

If someone summarizes that as "unsafe", then perhaps its not precise. But they might really mean "not as safe as another option I have using the same decompression time". Then it's fine.

Allright, first let me just say I've had quite a few conversations with people who were under the impression that deep stops were "debunked" and "unsafe", because "science" or "NEDU", based on forum exchanges;
Not "trials indicate that deep stops are probably overemphasised by bubble models such as VPM but we don't know exactly by how much".
There's a huge difference, and that's what I'm on about. I don't really think that's a radical notion.
I don't think you'll disagree with me insofar.

Now, let me further point out that I understand the difference between principally seeking the optimal decompression line, and practical application considerations, and am not mixing up those two.
That is, I can accept a certain deep stop level as too emphasised in terms of physiology, and still do them because of logistics. I see no conflict there.

Please note that I'm not calling deep stops safer or advocating pure bubble models.
Conversely, the indications we have - while certainly strong enough to form a reasonable working hypothesis - personally, I think they're still vague and leave room for further questions, discussions and trials.
I don't think there's anything controversial in that view. I don't think that's even dismissive.

Let me put it this way. If I heard someone say, "Deep stops are unsafe" and another person say, "Deep stops are not unsafe and you have to use GF100/100 if you say that" I would conclude that it was person 2 who didn't understnad the "ins and outs of the debate."

If I say to you that gas mechanics are no factor in decompression, the only other mechanism of decompression you'd have to offer, is tissue gas supersaturation, right?
I know it's crude, but if that's the case, logically, m-values pure would be the logical approach.

A crude retort to a crude statement, I admit. But it's because:

Actually, though, bubble mechanics is not out the window.

And I don't disagree with you that the physiological "ultimate answer" is probably somewhere in the middle. That's why I find the notion that gas mechanics have no impact to be absurd.

On a finishing note, an appeal. Please don't mistake the above for a notion that present bubble algorithms account ultimatively better for the physiological processes we're hoping to have illuminated.
Please understand that when I stop deeper, it's not religion versus science - it's pretty much just logistics.

 

[Cowfish Aesthetic]

let me just say I've had quite a few conversations with people who were under the impression that deep stops were "debunked" and "unsafe", because "science" or "NEDU", based on forum exchanges

Go argue with them and leave the informed debate here alone. You've been arguing against ghosts since the beginning.

 

[UWSojourner]

Allright, first let me just say I've had quite a few conversations with people who were under the impression that deep stops were "debunked" and "unsafe", because "science" or "NEDU", based on forum exchanges;
Not "trials indicate that deep stops are probably overemphasised by bubble models such as VPM but we don't know exactly by how much".
There's a huge difference, and that's what I'm on about.

Why would you say the difference is "huge"??? Both statements would lead me away from using, for example, VPM or RGBM and toward using something like GF40/X. Both statements would imply that the current state of research says the deep stops generated by common bubble models are likely causing additional risk to a profile (aka "unsafe"???). I see a difference in common usage vs. a scientific statement, but I'm not sure why you label it "huge".

Conversely, the indications we have - while certainly strong enough to form a reasonable working hypothesis - personally, I think they're still vague ...

Obviously we disagree. ALL the research we have is indicating that the deep stops commonly generated by models like VPM-B, RGBM are counterproductive to safety. That's not vague. That's pretty clear. It's clear enough that researchers are making statements like this:

"The impact of deep stops is not that they target some different physical reality. It is actually quite simple; the extra time spent deep allows more inert gas uptake in the relatively undersaturated intermediate and slow tissues. This is simply a loading problem that subsequently produces a higher degree of decompression stress. If there is less uptake at depth, ascent to a relatively shallow stop has much less risk. The idea that deep stops controlled bubble growth is one of the armchair arguments that has not lived up to human testing ... As with all the protocols we developed and subsequently saw fail, it is time to respect the data over the hand-waving." Dr. Pollock

The research is pretty clear, the statement above is pretty clear.

Please understand that when I stop deeper, it's not religion versus science - it's pretty much just logistics.

If you're stopping because you MUST stop due to "logistics", then you're no longer discussing best decompression practices which has been the topic in these deep stops threads.

 

[tursiops]

Please understand that when I stop deeper, it's not religion versus science - it's pretty much just logistics.

What logistics cause you to do this?

 

[Dan_P]

Why would you say the difference is "huge"??? Both statements would lead me away from using, for example, VPM or RGBM and toward using something like GF40/X. Both statements would imply that the current state of research says the deep stops generated by common bubble models are likely causing additional risk to a profile (aka "unsafe"???). I see a difference in common usage vs. a scientific statement, but I'm not sure why you label it "huge".

Obviously we disagree. ALL the research we have is indicating that the deep stops commonly generated by models like VPM-B, RGBM are counterproductive to safety. That's not vague. That's pretty clear. It's clear enough that researchers are making statements like this:

"The impact of deep stops is not that they target some different physical reality. It is actually quite simple; the extra time spent deep allows more inert gas uptake in the relatively undersaturated intermediate and slow tissues. This is simply a loading problem that subsequently produces a higher degree of decompression stress. If there is less uptake at depth, ascent to a relatively shallow stop has much less risk. The idea that deep stops controlled bubble growth is one of the armchair arguments that has not lived up to human testing ... As with all the protocols we developed and subsequently saw fail, it is time to respect the data over the hand-waving." Dr. Pollock

The research is pretty clear, the statement above is pretty clear.

I would say the difference is "huge" because "less safe" and "unsafe" can be wildly conflicting.
Allow me to illustrate (please don't take these illustrations as an insult, I had to make do with what I had on hand. Humour me for a moment):

First, what we want to do, is gauge "safety" (or "efficiency" if you prefer), by a given metric, across varying levels of deep/shallow stop emphasis. Illustrated here:

Now, we could say that safety would be highest with some balance across deep/shallow emphasis...

...or we can just say that the line would look more like this (below). It doesn't really matter in terms of principle here.

Second, to get clearer results, we'll "stress" the architecture of the trial. That is, we drive the line south:
(e.g. cold, deep air diving, air decompression, etc.)

Now, we'll trial two different algorithms in that framework (blue and green).

This illustrates how the difference in safety across "blue" and "green" looks monumental in the zoomed in square above - but looking at the top/original line (in black), they're both 1) close to oneanother, and 2) safe.

Looking at the zoomed-in frame and deducting that "blue" is unsafe, seems potentially misperceiving to me.
"less safe", allright, but easy to misinterpret.
"suboptimal", sure, okay.

I feel that's more than semantics.

Now, if we talk about why the NEDU parametres were set up the way they were, I think Doolette did a fine job of explaining that, and I get it - but let's not disregard that the trial was stressed to show us something (whether deep stops were better or not). We all learned that with basis in this trial, they were probably overemphasised in the bubble models.
[note, this is where part of my motivation for using the word "vague" lies: we still don't know by how much]

But "unsafe"? I have reservations.

I have some other open questions about the study, but let's agree to keep this conversation more to the point we were discussing in terms of "unsafe" versus "suboptimal"

If you're stopping because you MUST stop due to "logistics", then you're no longer discussing best decompression practices which has been the topic in these deep stops threads.

My point with that is that I don't need deep stops to be "right" - that's more of an academic curiosum to me.
The implication is I'm more than open to look at reports, and pay the royalties to do so, and adapt with findings, and evolve as our cumulative body of knowledge does.
I don't have a problem with a shifting emphasis.

What logistics cause you to do this?

E.g. If I need to bring two divers from 50m to 6m from the end of the bottom portion because that's where my next gas is (oxygen) as I've planned to do that based on an (extremely shallow) "optimal" algorithm, it's a logistical issue.
I'd prefer nitrox 50, which I can deploy at 21m. Example of less bottom gas requirement.

E.g. If my buddy and I are diving, I'm on O/C and he on CCR, our gasses and asend profiles become identical, even if he bails out (maintaing a pp02=1.2 average on O/C). Example of system interoperability.

E.g. If I'm on deck and dive site A is out, I can skim our gear and gas, and have a new dive plan ready within 10 seconds. Example of ease of planning.

E.g. If I'm on the deepest part of a wreck and find life sucks there, I can adjust my plan and know exactly what I can do with the gas available to me if I hop up to the shallower portion, before I do so. Example of ease of adjustment.

E.g. If I'm teaching a team and I want to develop or control their level of awareness, I can see if/how they adjust their deco time based on various stimuli. Example of value as a training tool.